Cellulosic structure and method for preparing same



Patented May 23, 1939 UNITED srA'r -zs PATENT OFFICE onrmunosro STRUOTUBEANDMETHODFOR ranmamc SAME George H. Latham and James K. Hunt, Wilmington, Del., assignors, by mesne assignments, to

E. I. du Pont de Nemonrl & Company, Wilming ton, Del., a corporation of Delaware No Drawing. Application June is, 1935,

Serial No. 27,232

- 5 Claims. '(ol. 99-171) This invention relates to theinhibition of mold growth by means of a wrapping material which in cellulosic wrapping'materials where the latter are non-fibrous, smooth, dense, substantially non-porous, and preferably transparent. In

many instances the commodities so wrapped are subject to the development of mold and the wrapping, because of its density and nonporosity, may at times serve to incubate the mold spores and thereby contribute to or at least fall to retard the mold growth. Thus, for example,

'bread, wrapped in a regenerated cellulose wrapper and stored under conditions conducive to mold growth, may develop mold rather quickly. In the same way, fruit, such as oranges, may

develop mold despite the cellulosic wrapper.

Previous attempts have been made to prevent mold growth by treating the wrapping material with fungicides or the like. Such wrappers have, however, been inefl'ective where the commodity is already inoculated with mold spores, servingonly to protect the wrapperitself from developing mold in or on its structure. commodities themselves. have been treated with a fungicides, but this sort of treatment is obviously inapplicable to all commodities, particularly foodstufis, either because of the nature-of the commodity or the toxicity of the fungicide. Furthermore if the wrapper itself is not treated it is receptive to mold spores and their subsequent growth. In the case of transparent wrappers, mold growth on the commodity or the wrapper is not only undesirable insofar as the commodity is concerned but, even though the mold may do'no harm, it is repulsive to the consumer and the I result is an unsightly, unsalable package. In

many instances the treatments of the prior art involve odorous materials which impart odor or.

taste to the wrapped commodities and obviously I this is highly undesirable. f

In accordance with the present invention it has been found possible to provide a wrapping material which not only resists the development of mold in or on its structure but at. the same time Similarly the inhibits the growth of mold in or on thecommodity which may be wrapped therein, even though the commodity may have been inoculated with mold spores prior to wrapping. The wrapping material provided by this invention is, moreover, non-toxic and the edibility of foodstufis wrapped therein isin no wise affected. In the eventthat mold growth should develop within a package wrapped with the material of this invention, either because of the excessive supply of mold sporesin or on the commodity, as might be the case with bruised or damaged fruits, it is significant to note that the unbroken wrapper of the present invention will prohibit the passage of mold spores therethrough and consequently adjacent packages will not be contaminated, the mold growth being confined within the package in question.

-It is therefore an object of this invention to provide a cellulosic wrapping material capable of inhibiting mold growth either in or on its own structure and/or in or on the structure of articles or commoditieswrapped therein. It is a further object of this invention to provide a non-toxic mold inhibitive cellulosic wrapping material which is smooth, dense, nonfibrous, substantially non-porous and preferably transparent. More specifically it is the object of the invention to provide a mold inhibitive wrapping material comprising a pellicle of regenerated cellulose.

Other objects will be apparent in view .of the following disclosure.

The objects of the invention'are accomplished by treating. the base material which is to serve as the wrapper with amaterial which is a mold inhibitive agent or; which decomposes slowly to yield a mold inhibitive agent. In the practice of the invention sumclent quantity of the agent is employed to accomplish the desired degree of mold inhibition, while at the same timeavoiding such excess as will impart odor or taste to the wrapped articles. a

Asbase materials for the wrapper, the invention contemplates cellulosic pellicles which are smooth, dense, non-fibrous, substantially nonporous ,andpreierably transparent, such as may be obtained by coagulation and/or regeneration of aqueous cellulosic dispersions. Such pellicles include those of regenerated cellulose produced by the viscose or cuprammonium processes, glycol cellulose, cellulose glycollic acid, lowly esterified or lowly etherified methyl, ethyl or acetyl' cellulose or the like.

As the mold inhibitive agents the invention contemplates the use of formaldehyde, thioformaldehyde or substances which slowly and spontaneously liberate formaldehyde or thioformaldehyde. Included among such substances may be mentioned:

Similarlythe thioformaldehyde analogues may be used or other formaldehyde orthioiormalde- 2o hyde liberating materials. The mold inhibitive agents may be used singly, or two" or more of them may be used in combination with each other. i

It has, been found most convenient-to apply the agents fromsolutions containing a concentrati'on of the mold inhibitive agent ranging from 0.5 to althoughmost satisfactory results are usually obtained through the use of concentrations ranging from 1-5%. Obviously the concentration of solution will be chosen according to the potency of the agent and the type of wrapping material finally desired.

- It is usually desirable to incorporate a softener.

or flexibilizing agent, such as glycerol, glycol,

diethylene glycol or the like, in the cellulosic pellicle. This can be incorporated conveniently by adding the softening agent to an aqueous bath solution containing the mold inhibitive' agent. Obviouslythe pellicle will be treated after the'pellicle has been coagulated or regenerated,

purified and washed thoroughly and just before it passes to the drying apparatus, for otherwise either or both thesoftening and mold 'inhibitive agents would be washed out or diluted.

- Although itis usually preferable to apply the mold inhibitive agent by immersion of the pellicle in an aqueous bath, it is nevertheless equally eflicacious to apply the same from any desirable solvent solution by immersion, brushing, spray-' ing'or other known method of application.

The invention will be more clearly illustrated by reference to the following specific examples,

it being understood that the scope of the invention is in no way limited thereto.

y sam le 1 I A sheet of plain regenerated cellulose sheet-- .ing, softened or not as desired, is immersed in the following composition which is maintained 7 60 at a temperature of about 35 C.

Parts by weight Water 89.0 'Gelatin 5.0 5 G1YOBI'01 v 5.0 :-.-Formaldehyde -i.0

After removal item the solution. the sheetis allowed to drain or is passed between squeeze rolls whereupon it is hung vertically and allowed r te dry in air at a temperature or about 25-30 C. The dry pellicie is useful as a mold inhlbitive wrapping material. w r ll 'Ashoetofplsinregenerstedcellmosesheeting, softened or not as desired, immersed in a bath of the following composition which is conveniently maintained at room temperature or lower:

Parts by g weight Water mo Glycer l 5.0 Formaldehyde 1.0

After removal from the bath. the drained m sheet is allowed to dry while hung vertically air at room temperature.

Example 111 A sheet of plain regenerated cellulose sheet- 15 ing is treated as in Example 11 except for the use of the following bath composition: 1

- Parts by weight 20 Water $0.0 Formaldehyde 5.0 Glycerol 5.0

Where it is not important to soften the pellicle the following examplewill illustratethe treat- 9M,

ment;

Example IV A sheet of plain unsoftened regenegnt edcellulose sheeting is immersed in a bath of the *foilowing composition: r

' Parts b weight Water... 95.0 Formaldehyde 5.0 u

' The sheet is drained and dried in the usual manner.

. Example V The following bath composition may be substi-' tuted in Example IV if. desired:

Parts by weight- Water 7 90.0 Dimethylolurea 10.0 4

It is not essential that an aqueous treating. bath be employed and in many instances the use of a solvent other than water is desirable or required depending on the base or the mold inhibitive agent. Thus the base sheet may be. treated as follows:

'E'zample V:

A sheet of plain regenerated cellulose sheeting, softenedor not as desired, maybe treated with a bath of the -following composition:

Parts by wei ht Alcoho 95.0 Thioilormaldehyde 5.0

The sheet a then drained and dried ta usual. It is sometimes desirable to give the sheet a preliminary washingin the solvent employedin gs order to-insure complete even impregnation oi thetreatingbath.

' temple v11 For the bath composition of Example VI the 10 following may be substituted:

Parts by Alcohol g 05.0 lltdiethylaminomethmmethylmrestnu- 5.0 It

The invention is particularly adapted to the manuiactureoi celhfl'osic pellicles oi the type described bya continuous process. Thus, for example, in the manufacture of regenerated cellulose pellicles as by the viscose process, the viscose is extruded into asuitable coagulating and/or regenerating bath from which the cellulosic pellicle is led in continuous manner through puria ing operations, such as cutting, slitting, coating- .15

tying, bleaching and washing baths and then through a softening bath just before passingto a drier apparatus, from which latterthe pellicle is withdrawn in continuous fashion and conveniently wound in rolls suitable for further finishor the like. The instant invention'may bepracticed by adding the proper agents in suitable amounts to the softening bath or at least to the last bath prior to entry of the pellicle into the drier. The pellicle is then passed over drier rolls and collected in a well-known manner.

As has been mentionedabove, it isnot necessary to use aqueous treating baths for applying the mold inhibitive agent. When it is desired to use a non-aqueous treating bath, it is best to submit the pellicle to a seriesoi' baths to remove the water and replace it with the solvent of the treatingbath. Thus, for example, if an alcohol bath such as is described in' Examples VI or VIII is used, it will be best to replace the water 'in the pellicle with alcohol by passing the pellicle I through one or more alcohol baths prior to treat- 1 mentwith the mold inhibitive agent. Likewise.

. inhibitor'bath, the water may be replaced by i a water immiscible solvent is used for the mold washing with a water miscible solvent which is also miscible with the solvent 01' the treating I hath whereupon the water miscible solventcan be replaced by the water immiscible solvent.

If it is desirable to practice the invention as a may be led through a series of treating baths. It is best in practicing this embodiment of the invention to pass the pellicle through water to swell the cellulosic structure and insure complete subsequent impregnation. If desired the water or swelling agent may be displaced by other solvents 1 in the manner described above.

It is usually most convenient to practice, the invention in connection with gel cellulosic pellicles, that is, pellicles which havebeen cast, purifled, bleached and washed but not dried. Economies in practice are thus possible since rewetting, resoitening,'redrying, etc., are avoided. The invention, however, is not restricted to the use 01' gel pellicles.

Depending on the method chosen for treating the pellicles, i. e., continuous-or discontinuous,

the drying'conditions may vary. Except as it may speed up the process there is no need for drying. at an elevated temperature. In con- 1 present invention with some other treating process, suspensions of the mold inhibitive agents may a be used. The iollowing example illustrates the combination of the instant invention with a waxing operation.

.sheet. base pellicle from which the water has previously been displaced by toluene. The amount 7 following table:

continuous operation separate and distinct from the casting operation, theflnlshed, dry cellulosic pellicle as obtained from the casting machine,

s 3 I Emple vm A sheet of regenerated cellulose. softened or not as desired, is immersed in or sprayed with a The sheet is dried, preferably at a temperature above the melting point or the wax to produce a smooth surfaced; transparent or translucent This example may-be practiced, using a transparency oi! the product.

The efiectiveness of wrapping materials in providing the mold growth inhibition is shown by the Tabla- Bread mold Slices oi fresh bread were inoculated with mold spores and wrappedin regenerated cellulose pellicles treated in accordance with the invention. Controls were run simultaneously using similar regenerated cellulose pellicles which had not been treated=to inhibit mold growth.

Oranges, inoculated with mold spores, were wrapped in regenerated cellulose pellicles .treated with the composition of Example III. The.

oranges wrapped in the treated pellicles showed no molding after two months storage whereas controls in which the wrappin material was untreated regenerated cellulose sheeting had molded after three days 'aging under similar conditions. Similarly good results are obtained using thevcompositions of Examples V, VI, and VII in place 01 Example III above.

The products of the invention are remarkably stable and may be stored for long periods of time between manufacture and use without appreciable loss of eil'ectiveness. Even prolonged heating does not remove the mold inhibitive agent as is evidenced by the fact that a sample prepared in accordance'with Example I, for instance, after seven weeks storage at ordinary temperatures, followed by 25 minutes heating at 100 C. in an air oven, still showed a strongly positive test for formaldehyde. Similarly pellicles treated as in Example'II, dried in air overnight and heated for 25 minutes at 100 C. in an air oven, gave a test for iormaldehyde substantially as strong as a test prior to heating. .The products also show no tendency to develop any appreciable odor even on long storage. Thus, samples preserved in a closely packed condition gave no detectable odor after having been left undisturbed for seven weeks.

The invention has been described with particular regard to transparent colorless pellicles but it is within the scope of the invention to treat colored, opaque, pigmented, printed or other pellicles where these qualities, are desired. Prefsizing or the like.

ly the treatment of the instant invention in no way interferes with any subsequent treatments which may be given the pellicle such as coating,

Obviously. a superficial coating will decreasethe effectiveness of the pellicle as a mold inhibitive wrapper but will not interfere with the protection against mold growth within the wrapper itself or the eflectiveness of the wrapper in preventing contamination of other adjacent packages. Many changes and modifications of the invention as above described may obviously be made without departing from the nature and spirit of the invention. It is therefore to be understood that the invention is not to be limited thereto except as set forth in the appended claims.

We claim: v.

1. The method of packaging commodities which comprises treating a regenerated cellulose pellicle with a solution of a mold inhibitive agent of the class consisting of formaldehyde and thioformaldehyde, drying the same, and applying the pellicle 'to the wrapping om commodity which is susceptible to mold growth, said mold inhibltive agent being present in the pellicle in a concentration so small as not to impart taste or odor to the commodity, but suflicient to prevent mold growth.

2. The method of packaging commodities which comprises treating a regenerated cellulose pellicle with a 05-20% aqueous solution of a mold inhibitive agent of the class consisting of formaldehyde and thioiormaldehyde to incorporate therein an amount 0! the said agent such that I which comprises treating a regenerated cellulose pellicle with a solution ofa mold inhibitive agent oi the class consisting offormaldehyde and thioformaldehyde, drying the same at an elevated temperature, and applying the pellicle to the wrapping ofcommodities which are susceptible to'mold growth. said mold inhibitive agent being present in the pellicle in a concentration so small as not to impart taste or odor to the commodity, but sufficient to prevent mold growth.

4. The I method of packaging commodities which comprises treating a regenerated cellulose pellicle with a solution oi formaldehyde, drying the same and applying the pellicle to the wrapping of a commodity which is susceptible to mold growth, the formaldehyde being present in the pellicle in a concentration so small as not to impart taste or odor to the commodity but suificient to prevent mold growth.

5. The method of packaging commodities which comprises treating a regenerated cellulose ,pellicle with a solution of thioiormaldehyde. drying the same and applying the pellicle to the wrapping of a commodity which is susceptible to mold growth, the thioformaldehyde being present in the pellicle in a concentration so. small as not to impart taste or odor to the commodity but suflicient to prevent mold growth;

- GEORGE H. LATHAM.

JAMES K. HUNT. 

